Telephone-exchange system



(No Mbdel.) 4 Sheets-Sheet 1A 1-1, T. GREENPIELD. TELEPHONE EXCHANGESYSTEM- No. 256,432. 7 Paten ted Apr. 11,1882.-

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( No Model.) 4 Sheets-Sheet 2.

E. T. GRB ENFIELD. v TELEPHONE EXCHANGE SYSTEM.

110.256.4552. Patented Apr. 11,1882.

227, Lav 026751:

(No Model.) 4Sheets-Sheet3.

E. T. GRE-ENPIELD.

I TELEPHONE EXCHANGE SYSTEM. No; 256,432. Patented Apr. 11, 1882.

Wi nesses.-

" g 1 nvenT02' UNITED STATES PATENT OFFICE,

EDWIN T. GREENFIELD, OF BROOKLYN, N. Y., ASSIGNOR OF ONE-HALF TO THEHOLMES BURGLAR ALARM TELEGRAPH COMPANY, OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Iietters Patent No. 256,432, dated April11, 1852.

Application filed April 23, 1880. (No model.)

To all whom it may concern:

Be it known that I, EDWIN T. GR-EENFIELD, of the city of Brooklyn andState of New York, have invented a new and useful Improvement inTelephone-Exchange Systems and Apparatus therefor, of which thefollowing is a specification.

The present invention relates to the construction and arrangement ofapparatus to be used in a central telephone-office, whereby exchangesbetween the various customers and offices connected with such centraloffice can be ett'ected quickly, easily, and economically; and theprincipal features of the invention are the use of a switch-boardprovided with a local ground, the combination, with. a switchboard, ofmultiple receiving and transmitting instruments, and a series ofautomatic drops or equivalent signal devices arranged in combinationwith the switch-board and the listening-oft' apparatus, all as morefully herein after set forth and claimed.

In the accompanying drawings, which fully illustrate this invention,Figure l is a general 2 5 perspective view of the combined apparatus,

S B indicating the switch-board, it the multiple receiver, T themultiple transmitter, and L O the listening-oft mechanism, consistingofa series of automatic drops, a key-board, and an 0 ordinary telephone.The switch-board, vfor convenience of illustration,is shown of smallersize relatively to the other parts than would occur in actual use. Forthe same reason the transmitter, the receiver, and the listening-oftapparatus are shown in closer proximity to the switch-board and to eachotherthan would be found convenient for practical purposes.

Fig. 2 is a rear View of the switch-board, showing the switches and thewires of the 10- 0 cal ground, as well as the general wiring of theboard.

Figs. 3 and 4 are side elevations of one of the switches, Fig. 4 showingthe position of the parts with the switch-plug P in place, and

7 5 Fig. 3 the parts with the plug removed.

Fig. 5 is a sectional view of the compound receiver, showing two of themagnets, Fig. 6 being a plan of the same receiver with the cap anddiaphragm removed.

Fig. 7 is a perspective of the compound transmitter, the hinged door orcover which carries the mouth-piece, the diaphragm and. the connectedparts being thrown open and a portion of the case being broken away, soas: to show the interior of the instrument.

Fig. 8 is a longitudinal section through the key-board and one of thedrops, showing also the connection of these parts with the switchboardand with the earth.

These drawings represent the improved ap- 6o paratus as arranged for usein connection with the service-lines of eight subscribers or enstomers;but the system may be applied to any desired number of lines.

'Referring to the several divisions of the apparatus more in detail, thereceiving-instrument R, to which all the service-lines pass. afterleaving the switch-board, is a multipleinstrument constructed on thegeneral plan illustrated in Figs. 5 and 6, in which there is 79 shown asingle diaphragm combined with a multiplicity of magnets and coils, thenumber of coils being one-half the number of lines in the system. Toefiect this the lines are connected with the instrument in pairs, eachpair of conductors beingjoined to a common coil. So far as concerns thismultiple receiver, the present invention relates to the coupling of twoconductors upon a single coil or spool, the use generally of amultiplicity of magnets or 80 of coils in a single receiving-instrumentbeing the special subject of another application for patent, heretoforefiled by me, and therefore not claimed herein. As fully explained insuch prior application, the use in asingle receiver 8 5.

of a number of separate magnetsror coils, orequivalent devices, enablesa single listeneron to keep watch over aud'reeeive orders from a largenumber of lines. The transmitter T is also a multiple or compoundinstrument, containing a single mouthpiece and diaphragm and one-half asmanyinduction-eoils as there are customers in the system, the secondarywires of the several coils uniting the service-wires in pairs inlikeman- 5 ner as they are united in pairs by the coils of the receiver. Themouth-piece and diaphragm, and the parts more immediatelyconnectedtherewith, may be of any ordinary construction, and therefore are nothere shown in i detail. So far, again, as concerns this multi-l pletransmitter, the present invention relates only to the coupling of twoconductors upon a single induction-coil, the use generally in atransmitter of a multiplicity of inductioncoils or equivalent devicesunder the control of a common diaphragm being the special subject ofanother application, filed by me contemporaneously herewith, andtherefore not claimed herein.

The switch;board S B consists in partof an upright frame provided withthe usual metallic union'strips, A B O D, arranged horizontally upon itsface, and with vertical metallic strips upon its rear, the latter beingso arranged relatively to holes passing through the former and throughthe board that metallic plugs inserted in such holes will bear againstthe elastic flanges ot' the vertical strips and thus enable the operatorat pleasure to establish electrical connection between any one of thefront and any one of the rear set of strips.

E is the main wire of a local ground-connection, leaving theswitch-board at any convenient point, as F, and grounded at G. From thismain wire E branch wires are run to each of the switches S S S 810. Theswitches are each composed of three projecting lips or flanges, l I l",of elastic sheet-brass or other equivalent material, so arranged thatthe insertion ot' a metallic pin or plug of the proper size through anyof the lower series of holes in the switch-board will press the lip Zaway from the lip I, as shown in Fig. 4, while the withdrawal of theplug will permit such lip to spring back into contact with Z, as shownin Fig. 3. Moreover, the lip Z is so related to the lip I that after theswitch-plug is inserted between them, as above indicated, it bearsagainst them both, and thus establishes an electrical connection betweenthem, such connection in turn being broken when the plug is withdrawn.

. The customers lines are represented by 1,2, 3,4,5,6,7,and S, and thewiring of the'switchboard is as follows: From the several binding-poststhrough which these lines enter the switch-board the wires pass to thecorresponding vertical strips, 1 2 3, 850., and thence to the uppermember, I, of the switches. From the lower member, 1, of the switchesthe wires 1" 2 3 &c.,run toasecond set of binding-posts, and afterleaving these last named posts the wires are looped together in pairs-1with 2, 3 with 4, &c.-each-loop being passed through the transmitter andthe receiver.

From the above explanation of the construction of the apparatus itsoperation will be apparent. Vhen the switch-plugs are all in place inthe switches S S, &c., each customers line is in connection, through theswitchboard, with both the receiver and the transmitter, and throughthese with the ground of that line to which it is itself coupled. Itfollows that any customer can at any time call the central station bysimply throwing his telephone into circuit with his special line in theusual way, and, also, that when he has thus put himself in communicationwith the central station he can hear any message that may be spoken intothe multiple transmitter, whether intended specially for him or foranyother person. It, now, any customer, as No. 3, desires to communicatewith any other, as No. 6, he calls the central otfice and gives hisorder, as 3 on 6. The switchman receiving the order from the listener-ondisconnects No. 3 from No. 4 and No. 6 from No. 5 by removing the plugsfrom the switches S and S of lines 3 and 6, and inserts these plugsdirectly above in any one of the horizontal union-strips, as B, whichmay happen at the time to be unoccupied. In this way the lines of No. 3and No. 6 are connected, each taking the ground of the other, and No. 6being rung up, everything is in condition for the transaction ofbusiness between them. Although by this arrangement No. 4 has been outoff from the ground of No. 3, and in like manner No. 5 from the groundof No. 6, yet the closing of the lips l l of the switches of lines 3 and6 consequent upon this withdrawal of the switch-plugs has thrown lines 4and 5 onto the local ground E, and as these lines still pass through thetransmitter and the receiver communications can take place freely overthese lines to and from the central ofiice.

The great advantage of thus coupling up the lines in pairs, which seemsto be rendered practicable only by the use of the local ground, is thatthe multiple instruments-the receiver and transmitter-can be made morecompact than would otherwise be possible, and thus a larger number oflines be brought under the control of a single operator or set ofoperators.

The mode of ringing up the customers when two are to be connected forpurposes of communication is as follows: After the two are plugged in onone of the horizontal unionstrips, as above explained, such strip istapped several times with the key K. This key forms one pole of a localbattery, and each time it touches the strip a current dividing at thepoint of contact passes over each of the two customers wires and ringsabell, or otherwise sounds an alarm,in the otfice of each customer. Thisis notice to the calling customer that he is connected with the persondesired, and is ,notice to the called customer that he is connected withsome one who desires communication with him, and thereupon the calledcustomer throws his telephone into the line and hails such other person.Manifestly, also, instead of using a battery with which to excite thelines for signaling the customers, an induced current might be similarlyutilized by means of a key, K.

The listening-off apparatus is constructed and operates as follows: Eachof the horizontal union-strips A B O D of the switch-board iselectrically connected with a corresponding key, A B, &c., upon thekey-board by wires arranged in any suitable manner. The contact-pointsof these several keys, when the keys are depressed, touch a metal strip,H,

IIO

the switch board.

which is connected through the binding-post I with the earth, and at anyconvenient point in this earth-connection there is placed an ordinarytransmitting and receiving instrument, J. From the wires that connectthe unionstrips of the switch-board with the several keys of thekey-board branch wires diverge and pass to corresponding drops, A B,&c., which are placed convenient to the keyboard, and from these dropsother wires lead down to the earthconnection of the key-board.In'practiee there should be as many drops as there are unionstrips onthe switch-board; but in the drawings, Fig. 1, only two drops are shown,one of which, D, has its cover up, indicating that the correspondingstripis not in use, whilethc other, B, has its cover down, displayingthe letter B,which indicates to the listener-oft that two customers areplugged onto the corresponding strip.

L'L is an electro-magnet having an armature, M, mounted upon or formingone end of a pivoted lever, the other end of which is notched to holduprthe cover of the drop, which is readily accomplished so long as thearmature is out of contact with the magnet.

The moment a cur-rent passes through the coil and magnetizes thesoft-iron core the armature is drawn down, and this elevates the notchedend of the arm attire-lever and releases the cover, which immediatelyfalls and displays a number or a letter like that which distinguishesthe corresponding union-strip of Each branch wire which leads oft fromthe connections between the switch-board and the key-board connects withone end of the coil of the electro-magnet of the corresponding drop, theother end of this coil being connected with the metallic frame of thedrop, and thus when the cover of the drop is raised an electricalconnection is secured, through such cover and the spring a, againstwhich the cover bears when raised, with the wire that leads from thedrop to the earth-connection of thekey-board, such wire being insulatedfrom the frame of the drop; but when the cover of the drop falls thecontact between it and the spring a is broken and the elect-ricalconnection through the drop is'destroyed.

From this construction it follows that whenever two service-lincs areplugged onto one of the union-strips of the switchboard, and a localcurrent is thrown onto such strip for signaling the two customers, asabove described, a portion of such current will also flow to the drop,and by exciting the electro-magnet will throw down the cover of thedrop, and thusindicate to the listener-oft that the correspon ing stripisin use. Thereafter it becomes the duty of the listener-off to keepwatch of the lines connected with the union-strip indicated by the dropand ascertain when communication between these lines has ceased,whereupon he is tonotify the switchman, who will at once disconnect thetwo lines and restore each to its normal connection with the switcharepassing between thelines which are shown by the drop to be jackedtogether upon any one of the union-strips is to depress the keycorresponding to such drop, which at once puts the telephone of thelistener-off into a branch circuit dtverging from the main circuitbetween the two customers who are electrically connected. By simplylisteningin his telephone the listener-off can ascertain whethercommunications between the customers have ceased. Thus one listener-offcan readily keep watch over a large number of lines.

It will be seen thatthe above system in its practical working is one ofgreat simplicity and efficiency. Three persons, at the central officecan readily take charge of a large number of lines and transact thebusiness with accuracy and without confusion. All the words that it isnecessary to have spoken at the central office are the repeating to theswitchman by the listener-on of the order which he hears in hisreceiver-as 3 on 6--and the order from the listener-off to the switchmanto disconnect any parties who have ceased talking, such order, forinstance, being, in brief, disconnectB, which signifiesdisconnecttheparties who are jacked onto union-strip B. Thus allconfusion at the central office, with the consequent danger of mistakes,is avoided. There is practically no chance of any custoniers who haveceased communication being cut off from the central office, as sometimesoccurs under some of the existing systems and three attendants in thecentral office can serveefliciently at least six times as many customersas would be practicable under one of the most generally adopted systemsin use at the present time.

I do not in this application claim the abovedescribed mode of ringing upand signaling customers by the use of a local battery, having withdrawnmy claim therefor, as originally filed, for the purpose of making thesubject thereof the basis of an application for a sepa* rate patent.

What is claimed as new is- 1. The combination,in a telephone-exchangesystem, of a plurality of service lincs with multiple receiving andtransmitting instru ments at the central station, each line beingconnected through the instrument with another line of the system,whereby each line normally or in a state of rest is grounded throughsuch other line.

2. The combination, in a telephone-exchange system, of a pl nrality ofservice-lines arranged in gronps,.so that in their normal condition or astate of rest each has as its ground the'ground IIO of some one of theother lines, a switch-board, and a local ground at the central station,arranged substantially as set forth, whereby any line out oif from itsnormal ground may take the local ground of the central station.

3. The combination,in a telephone-exchange apparatus, of a switch-board,a multiple receiver, and a plurality of service-lines leading throughthe switch-board to such receiver.

4. The combiuation,in a telephone-exchange apparatus, of a switch-board,a multiple transmitter, and a plurality of service-lines leading fromsuch transmitter to the switch-board, and thence to the customers.

5. The combination,in a telephone-exchange system, of two service-linesand a single coil in each of the instruments (the receiver and thetransmitter) of the central station, each line being connected throughsuch coils with the otherline,whereby each line normally orin a stateofrest is grounded through the other line.

6. In combination with the key-board of the listening-01f apparatus, aseries of automatic drops arranged and connected to be operated at thetime of placing, the customers in communication, substantially asdescribed.

7. In combination with the union-strips of the switchboard of a centraltelephone-station, a series of automatic drops arranged to be operatedby the same current with which the switchman signals the customers,substantially as set forth.

EDWIN T. GREENFIELD.

Witnesses:

H. F. NEWBURY, J AS. ToRNNEY.

